Scandium is very useful as an additive to high strength alloys and an electrode material for fuel cells. However, scandium has limited output and is expensive, and thus has not been widely used.
Incidentally, nickel oxide ores such as laterite ore and limonite ore contain a minute amount of scandium. In nickel oxide ores, however, the grade of nickel contained is low, and thus nickel oxide ores have not been industrially used as nickel raw materials for a long time. Therefore, the industrial recovery of scandium from nickel oxide ores has been hardly researched.
In recent years, however, the HPAL process is being put into practice, in which a leachate containing nickel and a leach residue are obtained by solid-liquid separation at a high temperature of about 240 to 260° C. after charging a nickel oxide ore into a pressure vessel with sulfuric acid. A neutralizer is added to the leachate obtained by this HPAL process to separate impurities, and a sulfidizing agent is then added thereto to recover nickel as nickel sulfide. The nickel sulfide is treated by an existing nickel refinement step to obtain electro nickel and nickel salt compounds.
When the HPAL process as described above is used, the scandium contained in nickel oxide ores is contained in the leachate with nickel (see Patent document 1). A neutralizer is added to the leachate obtained by the HPAL process to separate impurities, and a sulfidizing agent is then added thereto to recover nickel as nickel sulfide. On the other hand, because scandium is contained in the acid solution after adding the sulfidizing agent, nickel and scandium can be effectively separated using the HPAL process.
As a method for recovering scandium from the above acid solution, it is suggested that scandium is adsorbed on a chelate resin having an iminodiacetic acid salt as a functional group to separate impurities and is concentrated (see Patent Documents 2 to 4).
Incidentally, a method for recovering scandium from nickel oxide minerals using solvent extraction is also suggested (see Patent Document 5). In Patent Document 5, it is suggested that high purity scandium oxide is obtained by adding an organic solvent obtained by diluting 2-ethylhexyl sulfonic acid-mono-2-ethylhexyl with kerosene to an aqueous phase scandium-containing solution containing at least one or more of iron, aluminum, calcium, yttrium, manganese, chromium and magnesium along with scandium to extract scandium components into the organic solvent, then, in order to separate yttrium, iron, manganese, chromium, magnesium, aluminum and calcium extracted with scandium in the organic solvent, adding an aqueous solution of hydrochloric acid thereto for scrubbing to remove yttrium, iron, manganese, chromium, magnesium, aluminum and calcium, followed by adding an NaOH aqueous solution to the organic solvent to change scandium remaining in the organic solvent into a Sc(OH)3-containing slurry, dissolving Sc(OH)3 obtained by filtering this slurry in hydrochloric acid to obtain an aqueous solution of scandium chloride, adding oxalic acid to this to obtain scandium oxalate precipitates, filtering the precipitates to separate iron, manganese, chromium, magnesium, aluminum and calcium to the filtrate, and then calcining the precipitates.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. H03-173725
Patent Document 2: Japanese Unexamined Patent Application, Publication No. H01-133920
Patent Document 3: Japanese Unexamined Patent Application, Publication No. H09-176756
Patent Document 4: Japanese Unexamined Patent Application, Publication No. H09-194211
Patent Document 5: Japanese Unexamined Patent Application, Publication No. H09-291320